The present invention relates to high-speed turbine motors used in dental handpieces. In particular, the invention relates to the manner in which dental turbines are supported within the dental handpieces.
Dental handpieces having gas-driven turbine motors are well known. Of particular interest herein is a high-speed gas-driven dental handpiece having decreased noise and improved vibration damping characteristics.
U.S. Pat. No. 4,249,896 to Kerfoot, Jr. discloses a dental handpiece having a high-speed gas-driven turbine motor. A dental turbine motor of this type will rotate at speeds of over 400,000 rpm during use of the handpiece by a dentist. At such extreme speeds, minor imbalances may cause significant vibration and noise, which may impair the function and durability of the turbine and create discomfort and distractions to both dentist and patient. A support structure which provides noise and vibration damping to the turbine motor is thus desirable.
It is well-known in the art to provide first and second bearing assemblies to rotatably support a turbine motor within a dental handpiece, the first bearing being proximate a dental tool and the second bearing being distal the dental tool. From the Kerfoot, Jr. patent, it is further known to provide a single resilient ring, such as an o-ring made from a material such as neoprene, to capture an outer race of such bearings. The resilient ring provides radial support for the turbine motor assembly within the housing of the handpiece and substantially dampens the transfer of vibration from the motor assembly to the handpiece during use of the handpiece. Kerfoot, Jr. further discloses that a turbine motor assembly may include a spring washer which may be used to provide axial pre-load into the turbine motor bearing assemblies to further improve the dynamic characteristics of the device. More particularly, Kerfoot, Jr. discloses a single spring washer located at the first bearing assembly or first and second spring washers located at the first and second bearing assemblies, respectively. Kerfoot, Jr. does not disclose a single spring washer located only at the second bearing assembly.
A problem associated with the prior art, particularly the design disclosed in Kerfoot, Jr., is the difficulty in providing a method of supporting the outer race of a bearing assembly such that the outer race is prevented from spinning when the rotor and inner race are rotating. Spinning of the outer race of the bearing is detrimental to bearing life. A second problem associated with the prior art, again particularly the Kerfoot, Jr. design, is that a spring washer provided at the first bearing assembly proximate to the dental tool tends to experience excessive deflections, deform and flatten with use, lose the capability of providing axial pre-load and require frequent replacement.
There is need, therefore, for a high-speed gas-driven dental turbine having support structure which improves durability of the bearing assemblies while also adequately attenuating vibration of the rotor. There is a further need for a dental turbine having support structure which improves durability of support structure elements providing axial pre-load to the bearing assemblies.
According to one aspect of the invention, a dental handpiece for rotating a dental workpiece comprises a housing having a first end and a second end and a gas-driven turbine motor assembly including a rotor shaft having an axis of rotation substantially coincident with a central longitudinal axis of the housing. A chuck assembly secured to the rotor shaft, the chuck assembly releasably holding a shaft of the dental workpiece.
A first bearing assembly radially supports the motor assembly and is disposed toward the first end of the housing. The first bearing assembly includes:
an inner race fixed to the rotor shaft;
an outer race having an outer wall facing radially outwardly of the axis of the rotor shaft;
a plurality of movable bearing elements confined between the inner race and the outer race;
a first flange connected to a first end of the outer wall of the outer race, the first flange having a first lateral face disposed toward the first end of the housing and a second lateral face disposed toward the second end of the housing;
a first groove extending circumferentially about a second end of the outer wall of the outer race, the first groove lying in a plane substantially perpendicular to the axis of the rotor shaft;
a first snap ring retained within the first groove, the snap ring forming an annular-shaped collar extending radially outwardly of the outer race outer wall, the snap ring having first and second lateral faces, the first lateral face being oriented toward the first end of the housing and a portion of the first lateral face of the snap ring contacting a portion of the housing;
a first pair of resilient rings disposed between the second lateral face of the snap ring and the first lateral face of the flange and frictionally engaged with the outer wall of the outer race, each of the rings having an outer diameter sufficient to provide a compression fit between the outer wall of the outer race and the housing.
A second bearing assembly radially supports the motor assembly and is disposed toward the second end of the housing. The second bearing assembly includes:
an inner race fixed to the rotor shaft,
an outer race having an outer wall facing radially outwardly of the axis of the rotor shaft;
a plurality of movable bearing elements confined between the inner race and the outer race;
a second flange connected to a first end of the outer wall of the outer race of the second bearing assembly, the second flange having a first lateral face disposed toward the first end of the housing and a second lateral face disposed toward the second end of the housing;
a second groove extending circumferentially about a second end of the outer race outer wall of the second bearing assembly, the second groove lying in a plane substantially perpendicular to the axis of the rotor shaft;
a second snap ring retained within the second groove, the second snap ring forming an annular-shaped collar extending radially outwardly of the outer race outer wall of the second bearing assembly, the second snap ring having first and second lateral faces, the second lateral face being oriented toward the second end of the housing and a portion of the second lateral face of the second snap ring contacting the housing;
a single resilient ring disposed between the first lateral face of the second snap ring and the second lateral face of the second flange and frictionally engaged with the outer wall of the outer race of the second bearing assembly, the ring having an outer diameter sufficient to provide a compression fit between the outer race outer wall and the housing;
a substantially flat washer disposed between the ring and the second lateral face of the second flange;
a resilient spring-like spacer ring interposed between the second face of the second flange and the flat washer, the spacer ring transmitting a controlled compression force between the outer race of the second bearing assembly and the housing to provide axial pre-loading of the first and second bearing assemblies.